drivers: imx: uart: Add mxc_console

drivers: imx: uart: Add mxc_console

- Adds a simple register read/write abstraction to cut-down on the
  amount of typing and text required to access UART registers in this driver.

- Adds a console getc() callback.

- Adds a console putc() callback, translating '\n' to '\r' + '\n'.

- Initializes the MXC UART, take a crude method of calculating the
  BAUD rate generator. The UART clock-gates must have been enabled prior
  to launching the UART init code.
  Special care needs to be taken to ensure the UBIR is initialized before the
  UBMR and we need to ensure that UCR2.SRST comes good before trying to
  program other registers associated with the UART.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>